Electrolytic production of ticl4 and mg by means of a special anode



Feb. 13, 1962 lCHlRO EGAMI 3,021,268 ELECTROLYTIC PRODUCTION OF TIC AND Mg BY MEANS OF A SPECIAL ANODE Filed June 26, 1957 tats "trite This invention substantially relates to a method and corresponding apparatus for the continuous production of metal titanium from titanium compound selected from the group consisting of titanium dioxide, titanium hydroxides and mixtures thereof through chlorination and dechlorination.

It is a common practice to produce titanium sponges in such a way that titanium dioxide is chlorinated in a chlorinating furnace to titanium tetrachloride and the tetrachloride is supplied in drops onto a bath of magnesium fused in a reducing furnace made of iron to the desired products. This process has been known as the Kroll process.

An object of this invention is to provide a method and corresponding apparatus, capable of dispensing with the separate chlorinating step in the above mentioned process.

Another object of the invention is to provide a method and corresponding apparatus to produce metallic magnesium to be used for reducing titanium tetrachloride produced at the same time, at which the titanium tetrachloride is obtained.

Still another object of the invention is to provide a method and corresponding apparatus, capable of utilizing magnesium chloride resulted from the reduction of titanium tetrachloride by metal magnesium, again in the form of the bath necessary for the electrolysis.

A still further object of the invention is to dispense with means to recover or specially treat the waste gases, by the direct utilization of chlorine gas developing at the anode for said kind of effective usage.

Still another object of the invention is to provide a method and corresponding apparatus, to operate with higher thermal and working efliciencies than any conventional process and apparatus, by utilizing magnesium chloride in a recirculating manner.

According to this invention, the fused salt electrolysis of a mixture substantially consisting of magnesium chloride and sodium chloride is carried out by employing, on the one hand, a special anode comprising a baked mixture of a titanium compound selected from the group consisting of titanium dioxide, titanium hydroxides and mixtures thereof, capable of reacting with chlorine, mixed with carbonaceous substance, selected from a group of pitch, tar, pitch oil, graphite, cork powder and charcoal powder, and iron cathode known per se, on the other hand. In this process, chlorine gas developed from within the electrolytic bath reacts with the titanium compound contained in the anode to form titanium tetrachloride. The bath temperature is kept preferably about 700-800 C.

According to an aspect of the invention, thus obtained titanium tetrachloride reacts directly with metal magnesium, which has been separated at the cathodes during the electrolysis and now is floating on the bath surface, to form titanium sponges. The sponges are then refined in the usual manner to pure metal titanium.

In the above process, magnesium chloride in the bath is decomposed according to the following formula:

MgC1 Mg+Cl (1) When the anode contains, for instance, titanium dioxide,

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as the compound capable of reacting with chlorine, the following reaction will occur at the anode:

(TiO +2C)+2Cl =TiC1 +2CO 2 Thus produced titanium tetrachloride will react with metal magnesium floating on the bath surface, viz:

TiCl +2Mg Ti+2MgCl 3 Theoretically, the above mentioned process will continue, when the special anode is resupplied as consumed with the production of titanium sponges, while magnesium chloride recirculates in the reaction system without being consumed.

An apparatus especially adapted for carrying out said novel process may comprise: an electrolytic bath vessel made of heat-resisting material, preferably iron; an anode in the form of a solid cylinder comprising a baked mixture of titanium compound capable of reacting with chlorine; iron comb electrodes known per se; means adjustably to support said both kinds of electrodes; a hollow cylinder made of an insulating material, preferably bisque, and detachably attached to said anode, the last mentioned cylinder tightly covering a substantial portion of said anode, except upper and lower portions thereof; and a D.C. current source connected to said electrodes.

According to another aspect of the invention, the developed titanium tetrachloride and carbon monoxide gases at the anode are collected in a gas collector detachably attached to the anode. The gases are then led to a condenser, wherein the tetrachloride gas is condensed, while non-condensable carbon monoxide gas is discharged to the open atmosphere through an exhaust piping provided with a check point filled with a dehumidifier, such as CaCl The liquified titanium tetrachloride is accumulated in a liquid receiver and thence reintroduced again in the bath. However, in this case, the liquified tetrachloride is heated to gaseous state by a heating means, during passage through the supply piping leading from said receiver to the bath at a point lower than the bath level. Such heating preventspossible choking of the supply piping at the outlet to the bath. In most cases, the reintroduction of titanium tetrachloride is carried out by utilizing the action of gravity. It is natural, however, to arrange a pumping means in the supply means, if necessary.

The mixing ratio of titanium compound, on the one hand, capable of reacting with chlorine, and carbonaceous substance, on the other hand, may vary in weight between 1021 and 1:3.

An apparatus adapted to carry out the second mode of the novel method may comprise: an electrolytic bath vessel made of heat-resisting material, preferably iron; an anode in the form of a solid cylinder comprising a baked mixture of titanium compound capable of reacting with chlorine, such as the oxide, hydroxide and the like; iron comb electrodes known per se; means adjustably to support said both kinds of electrodes; an inverted cup-shaped gas collector made of an insulating material, preferably bisque and detachably attached to said anode; a D.C. current source connected to said electrodes; a condenser; piping means to connect the upper part of said gas collector to said condenser; a liquid receiver connected with said condenser; and further piping means to connect said receiver to said bath at a place lower than the bath level and provided with a heating means as well as at least a regulating valve.

According to a modified process according to this invention, the liquid titanium tetrachloride condensed in said condenser and accumulated in the liquid receiver is not returned to the electrolytic bath, but utilized for any other proper use. In this process, it will be clear that in the course of the electrolysis metallic magnesium and liquid titanium tetrachloride are continuously manufactured.

Various further and more specific objects, features and advantages of the invention will appear from the description given below, taken in connection with the accompanying drawings illustrating by way of examples two embodiments of the apparatus adapted to carry out the novel method, as well as with several numerical examples.

In the drawings:

FIG. 1 represents diagrammatically a longitudinal section of the preferred embodiment of the apparatus according to this invention.

FIG. 2 shows again diagrammatically in a longitudinal section a second preferred embodiment of the apparatus according to the invention.

Now referring to FIG. 1, 1 denotes the electrolytic bath vessel made of a suitable heat-resisting material, say, iron, as known per se. 2 represents iron comb elec trodes arranged at a distance from each other, each pref erably comprising a plurality of iron bars rigidly connected in a unit, again as known per se. 3 denotes an anode in the form of a solid cylinder comprising a baked mixture of titanium compound, on the one hand, such as the dioxide and/or hydroxide, capable of reacting with chlorine, and one or more suitable carbonaceous substance such as hereinbefore explained. A hollow cylinder 4 made of an insulating material, preferably bisque, is detachably attached to said anode 3, said cylinder tightly covering substantial portion of said anode, except upper and lower portions thereof being utilized as exposed conducting surfaces. This hollow cylinder 4 serves for preventing the separated and floating magnesium from shortcircuiting the anode. Although not shown, the anode as Well as the cathodes are adjustably supported by a hanging means, respectively. The anode and the cathodes are connected to a suitable DC. current source not shown.

When a mixture consisting substantially of magnesium chloride sodium chloride is charged into said vessel 1 and the electrodes 2 and 3 are energized, metal m-agnesium is separated in the usual manner at the cathodes 2, while at the same time chlorine gas developes at the anode 3, said gas directly reacting with the titanium compound contained in the anode to form titanium tetrachloride, which rises in bubbles up to the bath surface and reacts with the metallic magnesium floating thereon to titanium and magnesium chloride. The last mentioned reaction is accelerated by the bath temperature. T-hus produced magnesium chloride returns to the bath, while titanium is separated in the form of sponges, which in turn are refined to the desired metallic titanium as in the usual manner.

Next, referring to FIG. 2, 1 denotes the electrolytic bath vessel, 2 iron comb electrodes and 3 the anode, respectively, as in the preceding arrangement shown in FIG. 1. An inverted cup-shaped gas collector 4 made of an insulating material, preferably bisque, surrounds the anode 3 at the lower part thereof, and is provided with a discharge piping 6, which connects the upper space 5 of said collector 4 through a condenser 7 to a liquid receiver 8. From the bottom of said receiver leads a supply piping 9 to within the bath contained in the vessel 1. As shown by small arrows, the condenser 7 is cooled by means of a suitable cooling medium, such as water, recirculating through the condenser. The piping 9 is provided with a regualting valve 10 and a heating element 11.

In the fused salt electrolysis using the aforementioned apparatus, the chlorine gas developed at the anode 3 reacts with, for instance, titanium dioxide contained therein to form titanium tetrachloride according to the formula (2) as in the case of the preceding apparatus. Thus de eloped tetrachloride receives enough heat from the fused "bath and rises up in the gas state to the bath surface and is then collected within the inner space 5 of the collector -4. The gases consisting substantially of titanium tetrachloride and carbon monoxide are discharged through piping 6 to condenser 7, in which the tetrachloride condenses. The condensate is then discharged into the receiver 8, while non-condensable carbon monoxide is discharged through receiver 8 and exhaust piping 12 to the open atmosphere. The exhaust piping 12 is filled with CaCl in the U-bend, for the purpose of absorbing aqueous vapor contained in the air, which may sometimes enter into the receiver 8 in the reverse order.

When a suitable quantity of liquified titanium tetrachloride accurnul-ates in the receiver 8, the valve 10 is opened manually, or alternatively, automatically. As, in this case, the receiver 8 is situated at a relatively higher level than the fused bath, the tetrachloride is supplied by its own weight into the bath. In the course of this supply, the tetrachloride is heated sufiiciently by the heating element 11 and arrives at the bath in the gas state, resulting in a reaction with magnesium afioating on the bath surface to form titanium sponges and magnesium chloride, exactly as in the previous case.

As hereinbefore mentioned, the liquid titanium tetrachloride may be utilized for some other use, instead of being returned to the bath. In this case, metallic magnesium and titanium tetrachloride can be continuously manufactured.

Example 1 The apparatus hereinbefore explained referring to FIG. 1 was used, the anode consisting of a baked mixture of titanium dioxide about and carbonaceous substance about 15%. The anode was a solid cylinder having dimensions mm. 500 mm. The cathodes were iron combs, each comprising eight iron bars, 9 mm. The size of the electrolytic bath vessel was 400 mm. 400 mm. The insulating hollow cylinder detachably attached to the anode was made from bisque. Then, 60 kg. of charging mixture having a ratio, MgCl :NaCl=6:4 in weight, was introduced. Then, the electrodes were energized by the current from the power source, the current, 6-7 volts, amounting to about 200 amperes and thus the bath temperaturebeing kept at 700-800" C. and the charge being subjected to fused salt electrolysis. Metallic magnesium was, thus in the usual manner, separated at the cathodes and then came up to the bath surface. On the other hand, the chlorine gas developed at the anode and reacted with titanium dioxide contained in the anode to form titanium tetrachloride, which rose up in bubbles to the bath surface and reacted instantly with the floating magnesium, thus forming titanium dichloride and separating titanium sponges. Thus formed magnesium chloride returned to the bath and the above mentioned process was continuously repeated. The consuming rate of the anode was 4 mm./hr. In the course of 15 hours, 1.5 kg. of titanium sponges were obtained, the purity being 68.84% and the rest being Mg, Mgcl Fe, NaCl, C, Si, N and C1 The crude products were then subjected to vacuum distillation for purifying and 1.1 kg. of metallic titanium, purity 99.3% was obtained.

Example 2 In the preceding example, titanium hydroxide was used in place of titanium dioxide, and similar results were obtained.

Example 3 The apparatus hereinbefore explained with reference to FIG. 2 was employed. However, anode, cathodes, mixed charge, current conditions, bath temperature were just the same as in Example 1.

In this case, also titanium tetrachloride developed at the anode and accumulated in the collector 4. The tetrachloride gas was discharged through piping 6 to condenser 7, liquified therein and accumulated in receiver 8. When the tetrachloride liquid reached a certain height therein, the valve 10 was opened. The liquid was heated in piping 11 by heating element 11 to a temperature about 750 C. and returned thus in the gaseous state to the bath at a rate of 1.8 l. per hour, the pressure being 0.2 kg./cm. The tetrachloride gas reacted instantly with magnesium floating on the bath surface and titanium sponges were produced as in the preceding examples. The yield of sponges amounted to 1.6 kg. in the course of 15 hours and the purity was 70.84%. The constituents of the impurities were exactly the same as before. The crude products were refined as in Example 1 and metallic titanium, about 1.1 kg, purity 99.5%, was obtained.

Example 4 In place of titanium dioxide in Example 3, titanium hydroxide was used whereas the other conditions were the same. Similar result were obtained.

Example 5 The apparatus shown in FIG. 2 was employed. However, in this case, the valve was continuously closed.

Anode, cathodes, mixed charge, current conditions, bath temperatures were just the same as in Example 1. In the course of the electrolysis, metallic magnesium was, in the usual manner, separated at the cathodes and then came up to the bath surface, while the chlorine gas developed at the anode and reacted with titanium dioxide contained in the anode to form tetrachloride, which rose up in bubbles to the bath surface and accumulated in chamber 5. The gas was discharged thence through piping 6 into condenser 7 and condensed therein. The condensate was then accumulated in receiver 8 and conveyed to a certain place for some use, through a piping not shown. The waste gases, substantially consisting of carbon monoxide, were discharged through piping 12.

The yield of thus obtained metallic magnesium amounted to 85% and the purity of the metal was 99.6%. The yield of titanium tetrachloride was, on the other hand, 82.4% and the purity of the tetrachloride amounted to 99.5%. The current efliciency of the cathode was about 75%.

Although certain particular embodiments of the invention are herein disclosed for purpose of explanation, fur ther modifications thereof, after study of this specification, will be apparent to those skilled in the art to which the invention pertains. Reference should accordingly be had to the appended claims in determining the scope of the invention.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A process for upgrading titanium values and producing magnesium, which comprises electrolyzing a fused magnesium chloride-sodium chloride bath in the presence of an anode consisting essentially of a mixture of carbonaceous material and a titanium compound of the group consisting of titanium dioxide, titanium hydroxides and mixtures thereof, in the weight ratio of titanium compound to carbonaceous material between about 10:1 and about 1:3, so conducting said electrolysis that a layer of electrolyzed magnesium metal floats on the surface of the bath, removing the same from the bath, collecting electrolyzed chlorine at the anode and allowing the same to react with said titanium compound thereof to form a ti tanium tetrachloride-carbon monoxide mixture, removing the thus formed mixture from the vicinity of the anode and condensing titanium tetrachloride therefrom.

2. A process for producing titanium sponge in an electrolytic cell, which comprises electrolyzing a fused magnesium chloride-sodium chloride bath in the presence of an anode consisting essentially of a mixture of a carbonaceous material and a titanium compound of the group consisting of titanium dioxide, titanium hydroxides and mixtures thereof, so conducting said electrolysis as to permit magnesium collecting at the cathode to form a floating layer on the surface of the electrolytic bath, collecting chlorine liberated at the anode and allowing the collecting chlorine to react with the titanium compound of the anode to form a gaseous mixture of titanium tetrachloride and carbon monoxide, withdrawing said gaseous mixture from the vicinity of the anode, condensing titanium tetrachloride from said mixture and reintroducing the titanium tetrachloride to the electrolyte cell below the magnesium layer on the surface thereof whereby said titanium tetrachloride reacts with said magnesium to form titanium sponge and regenerate magnesium chloride.

3. A process as set forth in claim 2 wherein the elec trolysis is conducted at about 700-800 C.

4. A process as set forth in claim 2 wherein the condensed titanium tetrachloride is vaporized before it is reintroduced to the electrolytic cell.

5. A process as set forth in claim 1 wherein the titanium compound of the anode is titanium dioxide.

6. A process as set forth in claim 1 wherein the electrolysis is carried out at a temperature of about 700- 800 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,205,854 Kroll June 25, 1940 2,556,830 Thrune June 12, 1951 2,607,674 Winter Aug. 19, 1952 2,748,073 Mellgren May 29, 1956 2,760,930 Alpert et al Aug. 28, 1956 2,805,199 Banes et a1. Sept. 3, 1957 2,813,068 Steinberg Nov. 12, 1957 2,817,630 Dean Dec. 24, 1957 2,870,071 .Tuda et a1 Jan. 20, 1959 2,870,072 Merlub-Sobel June 20, 1959 2,870,073 Merlub-Sobel et a1 Jan. 20, 1959 2,943,032 Benner June 28, 1960 FOREIGN PATENTS 635,267 Great Britain Apr. 5, 1950 

1. A PROCESS FOR UPGRADING TITANIUM VALUES AND PRODUCING MAGNESIUM, WHICH COMPRISES ELECTROLYZING A FUSED MAGNESIUM CHLORIDE-SODIUM CHLORIDE BATH IN THE PRESENCE OF AN ANODE CONSISTING ESSENTIALLY OF A MIXTURE OF CARBONACEOUS MATETIAL AND A TITANIUM COMPOUND OF THE GROUP CONSISTING OF TITANIUM DIOXIDE, TITANIUM HYDROXIDES AND MIXTURES THEREOF, IN THE WEIGHT RATIO OF TITANIUM COMPOUND TO CARBONACEOUS MATERIAL BETWEEN ABOUT 10:1 AND ABOUT 1:3, SO CONDUCTING SAID ELECROLYSIS THAT A LAYER OF ELECTROLYZED MAGNESIUM METAL FLOATS ON THE SURFACE OF THE BATH, REMOVING THE SAME FROM THE BTH, COLLECTING ELECTROLYZED CHLORINE AT THE ANODE AND ALLOWING THE SAME TO REACT WITH SAID TITANIUM COMPOUND THEREOF TO FORM A TITANIUM TETRACHLORIDE-CARBON MONOXIDE MIXTURE, REMOVING THE THUS FORMED MIXTURE FROM THE VICINITY OF THE ANODE AND CONDENSING TITANIUM TETRACHLORIDE THEREFROM. 